1. Field of the Invention
This invention relates to the field of fluid-operated protectors for pipe threads, particularly in the oil-well industry.
2. Description of the Prior Art
Great shock loads are often created when the ends of oil-well pipe sections are dragged or slid to positions adjacent the well into which they are to be introduced. Furthermore, there frequently are enormous shocks when pipe sections are dragged or slid away from the well. In the absence of effective protection for the threads on the pipe sections, such shocks would often damage the threads and make the pipe unusable.
The shock loads are directed radially of the pipe, or longitudinally thereof, or a combination of the two. As an example of a longitudinal shock, a pipe may be so dropped or slid that it moves axially until its end crashes against a relatively hard surface.
When a pipe section is dragged, there are created powerful forces tending to rip the protector off the pipe end. These forces may occur, for example, when the pipe end reaches the transition point between a horizontal supporting surface and an inclined ramp. Unless the protector can withstand such forces, the pipe end will become exposed to damage as it is dragged or slid the remaining distance to the desired position.
Not only must the protector resist shocks, but it must be relatively immune to the great amount of wear which results from the dragging. In addition, the protector must be easy to mount and demount in a few seconds, must not be excessively heavy, and must be relatively universal in its operation.
Relative to the latter factor, universality, it is emphasized that "7-inch" (for example) pipe normally has the same outer diameter but may have distinctly different inner diameters, the inner diameters varying in accordance with pipe thickness and weight. A "7-inch" (for example) thread protector should be so universal as to fit on most seven-inch pipes, regardless of wall thickness and (very importantly) regardless of the type or class of thread which is present. There are various types or classes of threads, and it would be undesirable if each thread type made it necessary to use a different thread protector.
The optimum thread protector should also be relatively easy to manufacture, and to repair in the field. Pneumatic-type thread protectors should also be such that they will not leak even when subjected to extreme shocks, but will leak (instead of exploding) if air is inadvertently introduced prior to mounting on the pipe ends.
The prior art has not, despite thread-protector development over several decades, produced a thread protector which adequately satisfies all or even most of the above criteria.